The present invention relates to a photographic film cassette, and more particularly to the construction of a film passageway in the cassette, through which film is advanced.
A photographic film cassette for containing 135-type film is the most widely-used of the various film cassettes. This film cassette is constituted by a light-tight cylindrical cassette body having a film passageway and a spool rotatably contained in the cassette body, the film being coiled around the spool.
Light trapping fabric, or "plush", is attached to the inner surfaces of the film passageway for trapping light entering the cassette body through a film passage mouth. There are various types of plush, including: woven fabric and pile threads woven therein, as described in Japanese Utility Model Publication 37-21388; knitted fabric and pile threads woven therein, as described in Japanese Utility Model Publication 61-34526; pile threads planted on the film passageway, as disclosed in Japanese Utility Model Publication 37-4453, and Japanese Patent Laid-Open Publications 53-105222 and 57-190947; and non-woven fabric, as disclosed in Japanese Utility Model Laid-Open Publication 51-127737.
In the film cassette most generally in use, a film leader of the film coiled in a roll protrudes from the film passage mouth. However, a film cassette with the entire film roll contained in the cassette body up to a leading end of the film has been proposed recently. In this film cassette, rotation of the spool causes the film to advance outside the cassette body toward a film take-up chamber in a camera so as to wind the film on a take-up spool in the chamber, as disclosed in U.S. Pat. No. 4,832,275 and 4,834,306.
There is also a recently-used film cassette having a plastic cassette body. In FIG. 28, illustrating an important portion of this film cassette, opposing lateral sides of a film passageway in a cassette body are defined by both lateral walls 140 and 141, between which light trapping fabric 142 is attached to both inner surfaces of the film passageway. If the light trapping fabric is not attached precisely, gaps might appear between the lateral ends of the light trapping fabric 142 and the lateral walls 140 and 141. There could be a problem in that fogging might be generated on photographic film 14 when external light is incident on the inside of the cassette body 56 through the gaps. A proposed film cassette for solving this problem, described in Japanese Patent Laid-Open Publication 57-190948, provides extra fabric for trapping light attached to both lateral walls of the film passageway.
However, the light trapping fabric is attached to the film passageway so as to press the film between both pieces thereof in a self-advancing film cassette described above, the light trapping fabric is considerably resistant to film advance. Thus, the light trapping fabric might bend the film in the cassette body, stop the film from advancing, and damage film surfaces.
The pile threads of the above-described light trapping fabric occupy a larger space at their tops but a smaller space at the bottom, because the bottoms are bunched. Light is trapped reliably at the middle between the upper and lower surfaces of the film passageway, but incompletely in the vicinity of the upper and lower surfaces. In FIG. 29, external light entering the inner surfaces of the film passageway might be incident on the outermost turn of the film 14 without being trapped by the light trapping fabric 142. If the form of the film passageway has a large angle .THETA. between the external light incident on the film 14 and the tangent of the outermost turn of the film 14, there is a problem in that the light incident on the coiled film 14 can cause fogging on a number of turns of the coiled film 14. Also, a film cassette as disclosed in Japanese Patent Laid-Open Publication 57-190948 is too expensive, because two different types of light trapping fabric are necessary.